The present invention relates to a cathode ray tube subjected to an antistatic treatment and a method of making the same, and more particularly the invention relates to a cathode ray tube so designed that the electrified charge on the surface of a panel is leaked to a set chassis by means of a metal reinforcement, thereby preventing erroneous operations of the cathode ray tube and peripheral units and ill effect on the human body due to static electricity.
As a conventional antistatic treatment for cathode ray tubes, there has been proposed a method of making the surface of a panel of a cathode ray tube conductive as disclosed in JP-A-62-37850, and the desired antistatic effect has in fact been obtained by selecting the surface specific resistance of the panel less than 1.times.10.sup.11 .OMEGA. when the operating environment of the cathode ray tube has a humidity of less than 40-60% RH (Relative Humidity).
The technique disclosed in this prior art publication is such that in the cathode ray tube subjected to a non-glare treatment by forming a finely rugged and impressed surface layer on the outer surface of the face panel at the front of the glass bulb of the cathode ray tube, a thin silica film is additionally formed on the rugged and impressed surface layer thereby not only maintaining the desired non-glare effect but also enhancing the resolution and ensuring an excellent antistatic effect and electric shock preventing properties.
On the other hand, a technique of applying lithium silicate and forming a rugged and impressed coating on the surface of a cathode ray tube to ensure the desired reflection reducing effect and antistatic effect has been disclosed in a literature entitled "Lithium Silicate Antiglare Faceplate System For RCA Color Data Display Tubes", RCA, June, 1986, U.S.A. However, both of these prior art techniques have not gone to refer in detail to the grounding of the panel surface. When an insulation is provided between the panel surface and the metal reinforcement, that is, when the panel surface is not grounded, the surface specific resistance must be reduced to less than 1.times.10.sup.10 .OMEGA. in cases where the air-conditioned humidity is less than 40% RH during the operation of the cathode ray tube. There is another disadvantage that where the humidity is less than 20% RH, no great antistatic effect can be obtained even if the surface specific resistance is selected less than 1.times.10.sup.7 .OMEGA..
Also, there has been disclosed in JP-A-62-43042 a technique by which a front panel is applied to the surface of a face panel of a cathode ray tube by means of a transparent conductive adhesive resin prepared by mixing finely powdered silver, copper, carbon or the like into polyester resin and lead wires are brought out from the adhesive resin, thereby maintaining the front panel as well as the fastening metal members and the external conductive coating at the ground potential to prevent the face panel surface from being charged with static electricity. In other words, the adhesive resin is made conductive and the lead wires are connected to the adhesive resin, thereby ensuring the desired grounding.
In addition, JP-A-62-43043 has disclosed a technique by which a front panel composed of a conductive glass containing vanadium, etc., and having an electrical resistance of less than about 10.sup.3 -10.sup.9 .OMEGA.cm is applied to the surface of a face panel of a cathode ray tube with an adhesive resin and lead wires are brought out from the front panel, thus maintaining the front panel as well as the fastening metal members and the external conductive coating at the grounding potential and thereby preventing the face panel surface from being charged with static electricity. In other words, the front panel is made conductive and the lead wires are connected to the front panel, thereby ensuring the desired grounding.
With the methods disclosed in the abovementioned JP-A-62-43042 and JP-A-62-43043, however, the lead wires are connected through the terminals so that the areas of the connection portions are small and conduction failure tends to occur, thus making it difficult to connect the lead wires to the conductive member. Moreover, there is a disadvantage that even if the lead wires are connected, conduction failure tends to occur at these portions.